I had some of my old missions reset, namely the purging: The Purge, Purge Hunter, Purge Boss and Dungeon Purge. I had cleared all levels of these, but those were now all reset so it looks like I didn't clear any of them, and my cleared missions counter in the Achievements tab went back to 182.
(I did log in from a new device just prior to the update, it may also be connected to that rather than the update.)